This invention relates generally to a diaphragm fabricated on a substrate such as a silicon wafer or the like, and more particularly, to a metal diaphragm electroformed on a silicon wafer, having utility for a drop-on-demand (DOD) ink jet print head, a capacitive pressure sensor, and other applications wherein a metallic, conductive diaphragm can be used.
Currently, in micro electronic mechanical systems (MEMS), diaphragms are commonly fabricated from silicon, silicon oxide, silicon nitride and combinations of those materials. Shortcomings of such materials, however, include less than desired robustness compared to diaphragms fabricated from metals such as nickel. A silicon diaphragm also has cleavage planes and can be cleaved under some applications. Additionally, increasing the thickness of a silicon oxide or silicon nitride diaphragm has been found to increase the occurrence of internal stresses in the material, whereas by simply changing the integrated plating current, the thickness of an electroformed nickel diaphragm can be increased without a significant increase in internal stress.
Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact, low noise characteristics, its use of plain paper, and its avoidance of toner transfers and fixing. For these reasons, DOD ink jet printers have achieved commercial success for home and office use. DOD ink jet printers typically operate by subjecting a piezoelectric crystal to a high voltage electrical field, causing the crystal to bend, which in turn applies pressure on a reservoir of ink contained in an ink holding chamber of the print head via a flexible diaphragm, for selectably jetting ink drops on demand through an opposing nozzle or orifice. Typically, piezoelectric DOD printers utilize piezoelectric crystals in a push mode, a shear mode, or a squeeze mode. Piezoelectric DOD printers have achieved commercial success at image resolutions up to 720 dpi for home and office printers.
It is desired to fabricate a DOD print head using MEMS techniques which is operable for applying a pressure or acoustic wave to a reservoir of ink for uniformly lifting, raising or otherwise affecting the ink in an array of nozzles or orifices such that the ink can be selectably ejected through the nozzles or orifices using suitable conventional means, such as electrical impulse heaters or the like associated with the individual nozzles or orifices. However, to provide uniform ink ejection across the nozzles or orifices of the array, it has been found that the ink menisci in the respective nozzles or orifices must be uniformly affected by the pressure or acoustic waves.
It is believed that a primary cause of the inability to produce uniform waves is poor diaphragm function. Essentially, when the known diaphragm constructions are deflected or deformed into the ink holding chamber for lifting the ink, the diaphragms bend or bow across the length and width thereof, instead of moving as a unitary element. The bending or bowing of the diaphragm results in a domed structure with maximum deflection at the center, which does not produce a uniform pressure wave across the diaphragm. If a waveform produced in the ink is non-uniform, the ink menisci will be correspondingly non-uniform resulting in non-uniform ink droplet production.
Thus, what is required is a diaphragm for DOD ink jet print heads and other applications which moves or deflects as a unitary element so as to provide uniform pressure or acoustic wave generation characteristics.
An object of the present invention is to provide an improved diaphragm for DOD ink jet print heads and other applications which moves or deflects essentially as a unitary element so as to produce a more uniform pressure or acoustic wave, for example, in a body of ink in contact therewith to facilitate more uniform ink drop production.
With this object in view, the present invention resides in a diaphragm structure which includes a silicon substrate, such as but not limited to a wafer, having a surface and an opening therethrough, with a metal diaphragm electroformed on the surface and extending over the opening.
More particularly, the present invention resides in an ink jet print head including a support element defining at least a portion of a chamber for holding ink, the support element defining an opening adjacent to the chamber, and a diaphragm electroformed on a surface of the support element around the opening at least substantially covering the opening and enclosing the chamber.
According to an exemplary embodiment of the present invention, the diaphragm has a central region disposed generally centrally over the opening of the support element and a bellows surrounding the central region, the central region preferably being of greater cross sectional extent than the bellows such that the central region is substantially rigid and the bellows flexible. The central region of the electroformed diaphragm is disposed in contact with or connected to a piezoelectric transducer or actuator energizable for effecting reciprocal movement of the diaphragm for alternately contracting and expanding the volume of the ink holding chamber, producing uniform pressure or acoustic waves through ink contained in the chamber whereby ink menisci in nozzles of the print head in communication with the chamber are uniformly oscillated, lifted or otherwise affected.
To facilitate uniform wave generation, the central region of the diaphragm can be thickened relative to the bellows, and/or a stiffening member such as a portion of a silicon wafer mounted or attached thereto. Additionally, the diaphragm can be mounted or affixed to or otherwise brought into contact with the piezoelectric transducer or actuator for oscillating or reciprocating movement therewith. The bellows surrounding the central region of the diaphragm can optionally include one or more elliptical or other shape corrugations to facilitate flexure thereof for uniform displacement of the central region.
The present invention also resides in a method for forming a diaphragm for an ink jet print head, including the steps of electroforming at least one metal layer on a predetermined portion of a first surface of an etchable wafer such as a silicon wafer, etch masking a portion of the second surface of the silicon wafer to define an unmasked portion of the wafer underlying a predetermined portion of the at least one metal layer, and etching through the unmasked portion of the wafer to the at least one metal layer.
A feature of the present invention is the provision of a diaphragm of electroformed metal which is thin yet sufficiently rigid so as to oscillate without substantial deformation thereof, for generating substantially uniform waves in a body of ink or other fluid disposed in contact with one surface of the diaphragm.
Another feature of the present invention is the provision of a unitary diaphragm and surrounding bellows wherein the diaphragm is of greater cross sectional extent than the bellows.
Another feature of the present invention is the provision of an electroformed diaphragm including a stiffening member affixed or mounted thereto.
According to another aspect of the present invention at least one ink inlet channel can be electroformed on the surface of the support element in position for communicating with a source of ink external or internal to the print head. Additionally, the electroformed metal layer forming the diaphragm can include one or more openings or perforations therethrough for filtering ink that flows through the at least one ink inlet channel.
An advantage of the present invention is the ability to move the present diaphragm as a unitary element across substantially the entire length and width thereof for generating substantially uniform waves in a body of ink or other fluid disposed in contact with one surface of the diaphragm.
Another advantage of the present invention is the ability to produce a diaphragm in a manner that can be easily incorporated into conventional manufacturing processes for semi-conductor devices and MEMSs using silicon wafers and the like.
Another advantage of the present invention is the ability to form a unitary diaphragm and bellows wherein the diaphragm is of greater cross-sectional extent than the bellows.
Another advantage of the present invention is the capability to produce a diaphragm and at least one ink inlet channel communicating with a chamber for holding ink using some of the same manufacturing steps.
These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there are shown and described illustrative embodiments of the invention.